In some applications, a hysteresis circuit, also known as Schmitt trigger, can be used to convert an analog (or noisy) input signal to a digital output signal. The circuit has an output that retains its value until the input changes sufficiently to trigger a change. In some configurations, when the input is higher than a certain threshold, the output is high. When the input is below a different (lower) threshold, the output is low, and when the input is between the two levels, the output retains its value. This dual threshold action is called hysteresis and a hysteresis circuit can function as a bi-stable circuit such as a latch or a flip-flop.
Hysteresis circuits are typically used in signal conditioning applications to remove noise from signals used in digital circuits. They are also used in closed loop negative feedback configurations to implement relaxation oscillators, and are used in function generators and switching power supplies. A hysteresis circuit with a reliable hysteresis function is desirable.